Where did you get the idea that derivation necessarily had to involve a change in grammatical class? (Though it is easy enough to give examples that do show such changes, e.g. legal [adj] > legality [n]). Just because you've found (cherry-picked? LOL) some examples that don't show a change in class doesn't mean that they are examples of inflection.

The key thing is that with inflection the word-class does not (well, with the exception of certain uses of -ing forms) change, whereas derivation usually does involve a change* (=but may not always!).

Granted, I've arrived at these conclusions after just 5 minutes('?) checking in *Chalker & Weiner, but that's a pretty dependable resource!

Rules are rarely absolute, and thus need to be carefully written (see that 'usually' from C&W in my 2nd paragraph, and the bracketed corollary I've added after reading between the lines and extrapolating appropriately). No weasel words here.

Hi, fluffyhamster, I got the idea (derivation usually involves a change in grammatical class not in meaning) from some basic 'introduction to linguistics' books. While I was going through the book "Morphological Theory and the Morphology of English" by "Jan Don" last few weeks ago, I come across the examples "'cover' (v)-'uncover' (v)". Then I realized it. You are exactly correct that the basic books had given me the easy definitions of derivation and inflection. Thank you very much.

(derivation usually involves a change in grammatical class not in meaning)

Eh? You were postulating that without a change in class (even given the clear addition of affixes) derivation could not be involved, and said nothing (at least not explicitly) about changes in meaning (or the supposed lack thereof). But fine, no matter, I'd say that changes are always there, even in inflection (at least in terms ultimately of the necessary context), though not all morphology textbooks will go to the "pain" of repeatedly pointing this stuff out. As for derivation, the fact that un-s or dis-es or re-s or il-s or -ities or different classes come into play obviously makes at least the phrasings quite different (for example, compare 'legal war' with 'the legality of war', as in possibly 'Was the war legal?' versus 'The legality of the war can be questioned', and so on (the more basic wording seems more direct here)).

If that (what I've quoted above, especially the 'not in meaning' part) is what your textbook actually said or is causing you to believe then I suggest you either get a new textbook or stop reading stuff like it LOL. Or, I would look to actual words (in context) and stop lumbering yourself (and possibly others) with the theory too much. It is easy to get confused or start overthinking things, especially as many textbooks can be quite dry and ultimately not that good! (Assuming of course the fault lies with the authors ROFL!).

Derivation=word building. Inflection=not so much, just grammary-syntactic tinkering around their rear edges LOL.

Hello fluffyhamster, Thank you very much. I understand that I have to postulate the theory after referring many good and standard books only. Thank you very much for your efforts taken for me. Thank you so much.